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' RHEOSTAT.

No. 481,781. Patented Aug. 30, 1892.

UNITED STATES PATENT OFFICE.

CHARLES E. CARPENTER, OF MINNEAPOLIS, MINNESOTA, ASSIGNOR OF ONE- THIRDTO I. S. ANDREWVS, OF NEIV YORK, N. Y.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 481,781, dated August30, 1892.

Application filed February 18, 1891. Serial No. 381,825. (No model.)

To all whom it may concern:

Be it known that 1, CHARLES E. CARPENTER, a citizen of the UnitedStates, and resident of the city of Minneapolis, county of Hennepin, andState of Minnesota, have invented certain new and useful Improvements inRheostats, of which the following is a specification.

This invention relates to improvements in rheostats or resistances; andhas for its prime object to simplify the construction and reduce thecost of manufacture thereof, while at the same time rendering the devicemore durable and compact in form. This object is accomplished by thedevices illustrated in the accompanying drawings, in which-- Figures 1and 2 represent top plan views of rheostats embodying my invention withparts broken away, so as to more clearly show the internal constructionthereof; Fig. 3, atransverse vertical section of Fig. 1, and Fig. 4 adetail section taken on the line 3 3 of Fig. 1.

Similar letters of reference indicate the same parts in the severalfigures of the draw lugs.

Referring by letter to the accompanying drawings, A indicates abase-plate of some suitable metal for receiving a coating B of enamel orsimilar vitreous material which is adhesive and is a non-conductor ofelectricity. Many such materials, suitable for the purpose of myinvention, are now manufactured and applied to many kinds of utensils,generally in a plastic condition and fused for the purpose of attachingto the article, and sometimes are applied in a liquid or powdered state;but the process of manufacture of such material and the methods ofapplying the same form no part of this invention. In this coating isembedded a conductor or resistance C, preferably consisting of fine wireof the reflexed type, covering practically the entire surface of thebase-plate, the sections of which are by the coating of enamel orequivalent material secured firmly in position upon but insulated fromthe base-plate and correspond with the usual coils of a rheostat.

111 some kinds of work-such as electricallyoperated street-cars and insome electric-light systems-the rheostat employed may have a fixed andunchanging resistance which is predetermined, and therefore no meansneed be provided for altering or varying the resist ance of the same.IVhen such is the case, the instrument may be constructed, as shown inFig. 2, with any desired number of sections of the resistance orconductor, terminating at the ends, respectively, at the binding-post Cfor convenience in introducing the rheostat into the line-circuit, thenumber of' sections and the size and character of the conductordetermining the resistance offered by the apparatus. In other cases,however, it is desirable to have the rheostat so constructed as to beadjustable for varying resistances, as usual in this class of devices,and when such an instrument is required it will have the generalcharacter illustrated in Fig. 1, which I will now proceed to describe.In the coating of enamel is also embedded the connectorwire D, leadingfrom the pivot E of the switch-key F to the binding-posts G, as shown bydotted lines in Fig. 1, and also a series of contact blocks or plates11, arranged on the arc of a circle from the pivot of asWitch-key, andwith which such key makes successive contact in cutting out or in theresistance, each section being connected by the short wires I with acontact block or plate.

In the practical manufacture of these devices I have found it mostadvantageous to first coat the base-plate uniformly over its entiresurface, then set the various resistance coils or sections, wires, andcontact-blocks when used in position, and afterward applying one or morecoatings of the enamel or equivalent material, covering the wires, butleaving the upper faces of the contact blocks or plate exposed, theblocks for the greater security against displacement being provided witha lateral flange J around their base, which is covered by the enamel.

To prevent any undue heating of the base plate when heavy currents arepassed through the resistance, the back thereof may be ribbed,corrugated, or provided with a series of projections, as shown at K inFig. 2, which permits a free circulation of air around the back of theplate, and at the same time exposes a large surface for the radiation ofthe heat.

By my invention the cost of construction of rheostats or resistances isreduced to the minimum, while the simplicity, compactness,

and durability thereof is promoted to the maximum degree, the enamel orequivalent material serving to retain the resistance coils or sectionsin position against displacement, protects them from external injury,avoids the danger of fusion of the resistance, and perfectly insulatesthe coils or sections from their support and from each other.

Having described my invention, What I claim, and desire to secure byLetters Patent, 1s-

1. A rheostat or resistance comprising a base-plate corrugated, ribbed,or recessed on the rear face thereof and provided with a coating ofenamel or similar vitreous material on the front face and resistancecoils or sections embodied in such coating, substantially as and for thepurpose described.

2. Arheosl'at. nnmnrisino" a. base-late. nrnvitreous material, a seriesof resistance coils or sections, and a corresponding series ofcontact-blocks therefor embedded in such coating, and a switch-keyco-operating with such series of blocks, substantially as described.

3. A rheostat comprising, a base-plate provided with a coating of enamelor similar vitreous material, a series of resistance coils or sections,and connecting-wires embedded in said coating beneath the surfacethereof, but out of contact with the base-plate, a corresponding seriesof contact-blocks also embedded in said coating", but projecting beyondthe surface of the same, and a switch-key cooperating with series ofblocks, substantially 3 5 as and for the purpose described.

CHARLES E. CARPENTER. Witnesses:

A. (3. 711mm;

